Wiring method and apparatus for distributed control network

ABSTRACT

A multi-tier, master-slave control network having multiple buses comprises a master node and a plurality of slave nodes operating over each of the multiple buses. Each master node comprises a downlink transceiver, and each slave node comprises an uplink transceiver. All of the nodes in the control network are connected in a continuous loop configuration with each segment of the loop comprising a cable connector of either a first type (feed thru) or a second type (crossover). Each cable connector comprises a pair of signal wires for each bus. The type of cable connector between any two adjacent nodes in the loop is related according to which of the uplink or downlink transceiver should be connected to which bus.

BACKGROUND OF THE INVENTION

1) Field of the Invention

The field of the invention pertains to methods and apparatus forconnecting nodes in a control network having multiple data buses.

2) Background

Automated control systems are commonly used in a number ofmanufacturing, transportation, and other applications, and areparticularly useful to control machinery, sensors, electronics, andother system components. For example, manufacturing or vehicular systemsmay be outfitted with a variety of sensors and automated electricaland/or mechanical parts that require enablement or activation whenneeded to perform their predefined functions. Such systems commonlyrequire that functions or procedures be carried out in a prescribedorder or with a level of responsiveness that precludes sole reliance onmanual control. Also, such systems may employ sensors or othercomponents that require continuous or periodic monitoring and thereforelend themselves to automated control.

As the tasks performed by machinery have grown in number and complexity,a need has arisen for ways to exercise control over the variouscomponents of a system rapidly, efficiently and reliably. The sheernumber of system components to be monitored, enabled, disabled,activated, deactivated, adjusted or otherwise controlled can lead todifficulties in designing and implementing a suitable control system. Asthe number of system components to be controlled is increased, not onlyis the operation of the control system made more complicated, but alsothe wiring and inter-connections of the control system are likewise moreelaborate. In addition, greater reliance on automated control hasresulted in larger potential consequences if the automated controlsystem fails.

Traditionally, control systems in certain applications, such as transitvehicles and railcars, have relied upon relay-based control technology.In such systems, relays and switches are slaved to a logic circuit thatserves to switch signal connections. This approach requires a largenumber of relays and a substantial amount of wiring throughout thevehicle. In some instances distributed processors or logic circuits maybe used for subsystems such as the door, but these processors or logiccircuits often take up significant space and can be costly to maintain.

A substantial improvement has recently been made in the field of controlsystems. An improved network control system recently developed uses adual-bus architecture along with distributed controllers. In thisimproved network control system, a primary bus forms a high-speed,bi-directional communication link interconnecting a main data buscontroller with distributed slave modules, one of which acts as a seconddata bus controller connected to a secondary, low-speed data bus. Theslave modules are generally connected to various input/output ports. Thesecond data bus controller can be connected to second-tier slave modulesover the secondary, low-speed data bus. The main data bus controller,secondary data bus controller, first-tier slave modules, second-tierslave modules, input/output ports and other system componentscollectively form a hierarchical system wherein the main data buscontroller supervises the first-tier slave modules, including the seconddata bus controller, the second data bus controller supervises thesecond-tier slave modules, and the first-tier slave modules andsecond-tier slave modules supervise their assigned input/outputfunctions.

While the dual-bus control network as described above has manyadvantages, there are also ways in which it could be improved further.The dual-bus control network architecture as currently known in the artgenerally relies on a single top-level main data bus controller. If themain data bus controller fails, system performance will be adverselyimpacted. Also, the possibility of a short circuit occurring,particularly over a region of the bus, is a constant danger. In additionto disrupting communication signals among the components accessing thebus, a short circuit can be difficult to trace and cause substantialdisruption of system service while maintenance personnel attempt tolocate the short circuit. Furthermore, while the dual-bus networkcontrol architecture reduces wiring needed in a vehicle or otherautomated system, simplification of wiring connections would lead togreater ease of implementation and maintenance.

Accordingly, it would be advantageous to provide a network controlsystem that has a means for recovering from a failure in a main data buscontroller or otherwise mitigating the effects such a failure. It wouldfurther be advantageous to provide a network control system that reducesthe impact of a short circuit and enables rapid identification of thelocation of a short circuit by maintenance personnel. It would furtherbe advantageous to provide a distributed network control system withsimplified wiring and connections.

SUMMARY OF THE INVENTION

The invention provides in one aspect a technique for connecting nodes,such as master nodes and slave nodes, in a hierarchical, multi-buscontrol network.

In one aspect of the invention, a multiple-bus hierarchical controlnetwork is provided. A first-tier master node controls a plurality offirst-tier slave nodes using a first common bus for communication. Oneof the first-tier slave nodes is connected to a second common bus, andoperates as a second-tier master node for a plurality of second-tierslave nodes connected to the second common bus. Each master nodecomprises at least a downlink transceiver, and each slave node comprisesat least an uplink transceiver. All of the nodes in the control networkare connected in a continuous loop configuration with each segment ofthe loop comprising a cable connector of either a first type (feed thru)or a second type (crossover). Each cable connector comprises a pair ofsignal wires for each bus. The type of cable connector between any twoadjacent nodes in the loop is related according to which of the uplinkor downlink transceiver should be connected to which bus.

In a preferred embodiment of the invention, a master node serves as acontroller for a multiplicity of slave nodes. The master node polls theslave nodes periodically. Each of the slave nodes comprises a failuremode detector whereby, if a slave node fails to receive a message fromthe master node within a certain fixed period of time, then the slavenode takes over control for the master node.

In another aspect of the invention, prioritized redundant backup controlfor the master node is provided by establishing an order in which theslave nodes take over the master node, or substitute master node, in thecase of multiple node failures. Preferably, each slave node isprogrammed to detect a failure mode condition after a different amountof time than the other slave nodes are programmed with. When the firstslave node programmed with the shortest failure mode detection timedetects a failure mode condition, it takes over for the master node andbecomes the substitute master node. Should the substitute master nodealso fail, then the slave node programmed with the next shortest failuremode detection time will detect a failure mode condition and take overfor the substitute master node, becoming the second substitute masternode. Likewise, in turn each slave node has the capability of becomingthe master node when its programmed failure mode detection time elapses.In this manner, prioritized redundant backup control is achieved for themaster node.

Should a failure of the first-tier master node occur, any of thefirst-tier slave nodes connected to the first common bus can take overthe first-tier master node, doing so according to their programmedpriority. Should a failure of the second-tier master node occur, any ofthe second-tier slave nodes connected to the second common bus can takeover the second-tier master node, doing so according to their programmedpriority. Redundant master control is thereby provided for both thefirst tier and second tier in the hierarchical control network.

A preferred node comprises two separate transceivers, an uplinktransceiver for receiving control information, and a downlinktransceiver for sending out control information. Each node therefore hasthe capability of performing either in a master mode or a slave mode, orin both modes simultaneously.

Further variations and embodiments are also disclosed herein, and aredescribed hereinafter and/or depicted in the figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a distributed control network with two data busesas known in the prior art.

FIG. 2 is another diagram of a distributed control network having a twodata buses each configured in a loop configuration as known in the priorart.

FIG. 3 is a circuit block diagram of a node that may be employed in thedistributed control network of FIG. 1 or FIG. 2.

FIG. 4 is a diagram showing a physical encasement of the node shown inFIG. 3.

FIG. 5 is a block diagram of a preferred control network architecture inaccordance with one or more aspects of the present invention.

FIG. 6 is a block diagram of a preferred node within the control networkarchitecture shown in FIG. 5.

FIGS. 7A and 7B are diagrams of two different types of cable connectors.

FIG. 8 is a diagram showing an example of a distributed, multi-buscontrol network with control nodes connected in a loop configuration inaccordance with preferred aspects of the present invention.

FIG. 9 is a conceptual hierarchical diagram of the control network ofFIG. 8.

FIGS. 10A, 10B and 10C are more detailed diagrams showing theinterconnection of wires the cable connectors with the uplink anddownlink tranceivers of the control nodes of FIG. 8.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

This application is related to U.S. patent application Ser. No.08/854,160 filed in the name of inventor Jeffrey Ying and entitled"Backup Control Mechanism in a Distributed Control Network," U.S. patentapplication Ser. No. 08/853,989 filed in the name of inventor JeffreyYing and entitled "Multi-Tier Architecture for Control Network," andU.S. patent application Ser. No. 08/853,893 filed in the name ofinventors Jeffrey Ying and Michael Kuang and entitled "Fault Isolationand Recovery In A Distributed Control Network," all three of whichforegoing applications are filed concurrently herewith and herebyincorporated by reference as if set forth fully herein.

FIG. 1 is a block diagram showing the interconnection of nodes in aparticular type of control network 101 as known in the art. The controlnetwork 101 comprises a main data bus controller 103 which is connectedover a main data bus 104 to a plurality of first-tier slave nodes 109and 123. One first-tier slave node 123 connected to the main data bus104 also functions as a second data bus controller, and is connected toa second data bus 113. The second data bus controller 123 is connectedover the second data bus 113 to a plurality of second-tier slave nodes130. The main data bus 104 forms a high-speed, bi-directionalcommunication link between the main data bus controller 103 and thefirst-tier slave nodes 109 and 123, and the second data bus 113 forms alow-speed, bi-directional communication link between the second data buscontroller 123 and the second-tier slave nodes 130.

The nature of the slave nodes 109, 123 and 130 depends in part on thecontrol application for which they are deployed. In a transit vehicle orrailcar, for example, the master data bus controller 103 and the slavenodes 109, 123 and 130 may each be assigned to control a particularsection of the vehicle or railcar, or may be assigned to controlparticular input and output functions. For each slave node 109, 123 and130 in FIG. 1, various control signals are shown connected to the nodessuch as to illustrate one exemplary arrangement of controlfunctionality.

In operation, the main controller 103 communicates with the first-tierslave nodes 109 and 123 using the main data bus 104 as a high speedbi-direction link. An exemplary baud rate for communications over themain data bus 104 is 256 k. The main data bus controller 103 isgenerally responsible for delegating control commands to the first-tierslave nodes 109 and 123, and for responding to status information andevents communicated to the main data bus controller 103 over the maindata bus 104. Each of the first-tier slave nodes 109 and 123 receivescommands from the main data bus controller 103, and issues appropriatecommands over their respective control lines. In a similar manner, thesecond data bus controller 123 communicates with the second-tier slavenodes 130 using the second data bus 113 as a low speed bi-direction link(having a baud rate of, e.g., 9.6 k), and instructs the second-tierslave nodes 130 to carry out certain control functions, or responds tostatus messages or events relayed to the second data bus controller 123from the second-tier slave nodes 130.

FIG. 2 is a diagram showing the layout or architecture of the FIG. 1control network. The control network 201 shown in FIG. 2 comprises amain data bus controller 203 which is connected to a main data bus 204.The main data bus 204 is physically connected to a plurality offirst-tier slave nodes 209 and 223. As explained with respect to thecontrol network 101 shown in the FIG. 1, one of the first-tier slavenodes 223 also functions as a second data bus controller 223, and isconnected over a second data bus 213 to a plurality of second-tier slavenodes 230. The main data bus 204 is configured in a loop such that itpasses through each of the first-tier slave nodes 209 and 230 andreturns to rejoin the main data bus controller 203. In this way, shouldthe wires of the main bus 204 become severed, the main data buscontroller 203 will still be connected to the first-tier slave nodes 209and 223 and will not necessarily lose control over the system.Similarly, the second data bus 213 is configured in a loop such that itpasses through each of the second-tier slave nodes 230 and returns torejoin the second data bus controller 223, thereby providing anarchitecture resilient to potential severing of the wires of the seconddata bus 113. Each of the main data bus controller 203, first-tier slavenodes 209 and 223, and second-tier slave nodes 230 may be connected to aplurality of control signals for performing control or sensor functions,or various other input and output functions as necessary for theparticular control application.

The control network 201 shown in FIG. 2 thus utilizes a dual-busarchitecture to perform control functions. Because of the hierarchicalarchitecture of the control system 201, relatively low baud rates on thesecond data bus 213 can be tolerated, leading to reduced system size,cost and complexity over traditional non-hierarchical, relay-basedsystems. The slower speed on the secondary data bus 213 also reduces thesystem's susceptibility to electromagnetic interference, a potentialproblem in certain control system environments (such as railcars).

Each node, whether master data bus controller 203, first-tier slave node209 or 223, or second-tier slave node 230, includes means for performingcomputations necessary for its functionality, and is configured withcomponents such as a central processing unit (CPU) and memory. FIG. 3 isa more detailed block diagram of a node 301 (such as the master data buscontroller 203, a first-tier slave node 209 or 223, or a second-tierslave node 230) that may be employed in the control network of FIG. 2.The node 301 comprises a CPU 315 connected to a power control block 317and a transceiver 305. The node 301 is also connected to power signallines 316, which connect to the power control block 317. The node 301may communicate over communication signal lines 304, which are connectedto the transceiver 305. An electrical erasable programmable read-onlymemory (EEPROM) 306 stores programming information utilized by the CPU315 for carrying out certain programmable functions. The CPU 315 hasaccess to a random access memory (RAM) (not shown) and read-only memory(ROM) (not shown) as needed for the particular application.

The CPU 315 is connected to a keyboard and display interface block 320.The keyboard and display interface block 320 is connected to status LEDs307, relays 321, and LED display 311 and a keypad 331. The node 301 isthereby can accept manual inputs (e.g., from the keypad 331) or receivesensor inputs (e.g., over relays 321), and can display operationalstatus using status LEDs 301 or LCD display 311.

The node 301 further comprises a network controller 322 which preferablycomprises a second CPU. The network controller 322 is connected to asecond transceiver 323 which is connected to a second pair ofcommunication signal lines 314. The network controller also outputspower signal lines 336.

In operation, node 301 may communicate over two different data busesusing transceivers 305 and 323. Thus, node 301 may communicate over afirst data bus (such as data bus 204 shown in FIG. 1) by receiving andtransmitting signals over communication signal lines 314 usingtransceiver 323, under control of the network controller 322. The node301 may communicate over a second data bus (such as data bus 213 shownin FIG. 2) by transmitting and receiving signals over communicationsignal lines 304 using transceiver 305, under control of CPU 315. TheCPU 315 and network controller 322 may transfer information back andforth using a shared memory (not shown). The node 301 may serve as botha "slave" unit with respect to the first data bus 204 and a "master"unit with respect to the second data bus 213. By interconnecting aplurality of nodes 301 in an appropriate configuration, a hierarchicalcontrol network with two data buses (as shown in FIG. 2) may beestablished.

Each node 301 such as shown in FIG. 3 is housed in a rugged, potted casemade of a suitable lightweight material such as aluminum that providesenvironmental protection and allows for heat dissipation. FIG. 4 is adiagram showing an exemplary physical casing 401 of a module or node 301such as shown in FIG. 3. The casing 401 can be quite small; in theexample of FIG. 4, the casing 401 measures approximately 2.1" by 3.75",and is 0.825" in thickness.

A problem that can occur in operation of a control network such as shownin FIG. 2 is that if the master data bus controller 203 fails thenoperation of the entire system could be jeopardized. A possible solutionwould be to provide a redundant master data bus controller that has thesame functionality as the primary master data bus controller 203 in allrespects. Upon detecting a failure of the primary master data buscontroller 203, the backup master data bus controller could shut downthe primary master data bus controller 203 and take over control of thenetwork.

While having such a separate, redundant master data bus controller forbackup purposes may provide a solution where the primary master data buscontroller 203 fails, it falls short of being a complete solution. As anentirely separate controller having complete functional and hardwareredundancy of the primary master data bus controller 203, incorporationof the backup master data bus controller effectively doubles the cost ofimplementing the master data bus controller 203. Also, another drawbackis that if both the master data bus controller 203 the backup masterdata bus controller fail, then operation of the entire system would bejeopardized and operation could come to complete halt.

In addition to the possibility of the master data bus controller 203failing, the second data bus controller 223 could also be subject tofailure. While a redundant second data bus controller for backuppurposes could be provided, the cost of implementing the second data buscontroller would be essentially doubled, and the system is still subjectto potentially complete failure should the second data bus controlleralso fail. Moreover, adding redundant data bus controllers couldcomplicate the wiring of the system.

A preferred embodiment of the invention overcomes one or more of theabove problems by providing redundant backup control for the master databus controller 203 or other type of master node, the second data buscontroller 223 or similar types of nodes, and, if further nested controllevels exist (as described, for example, in later embodiments herein),other sub-controllers for those control levels.

FIG. 5 is a block diagram of a preferred embodiment of a control network501 having redundant backup control capability for a master node at eachbus level of the control network 501. Hereinafter, the node acting asthe master bus controller for a particular bus will be referred to asthe "master node" for that particular bus, and all the other nodes onthat bus will be referred to as "slave nodes" for that particular bus.In the control network shown in FIG. 5, a master node 503 and aplurality of first-tier slave nodes 523 are connected to a main data bus504. In a preferred embodiment of the invention, each of the slave nodes523 is configured or can be configured to control a secondary data bus.For example, the first-tier slave node 523c is shown connected to asecondary data bus 523 in the control network 501. The first-tier slavenode 523c functions as a second-tier master node with respect tosecond-tier slave nodes 533 connected to the secondary data bus 513.Others of the first-tier slave nodes 523 can also serve as second-tiermaster nodes and be connected to different secondary buses havingadditional second-tier slave nodes. A multi-level or multi-tieredhierarchical control network is thereby established.

Each of the master node 503, first-tier slave nodes 523, second-tierslave nodes 533, and other lower-level slave nodes (not shown in FIG. 5)are referred to hereinafter generically as "nodes" and are designated asnodes 530 in FIG. 5. In one aspect of a preferred embodiment as shown inFIG. 5, each of the nodes 530 has substantially the same hardwareconfiguration and can therefore function as either a master node or aslave node, depending upon how the control network 501 is configured.Each data bus, along with the nodes attached to it, are generallyreferred to as a cell, and the master node connected to the data bus isreferred to as a "cell controller" for that particular cell. Asexplained in more detail hereinafter, each node 530 configured as amaster node transmits and receives messages over the data bus for thecell it controls. Each node 530 configured as a slave node remains in alisten mode, receiving but not transmitting messages over that data bus,unless specifically requested to transmit information over the data busby the master node. Any number of the slave nodes can, even thoughoperating as a slave node with respect to an upper tier, besimultaneously operating as a master node with respect to otherlower-tier slave nodes at a different cell sub-level.

A preferred embodiment of the invention, as noted, comprises a mechanismfor redundant backup control of any node functioning as a master node atany level or sub-level of the control network 501. As generallydescribed, in operation of a preferred embodiment of the invention theslave nodes connected to a particular data bus monitor the data buswhile in a listen mode and await periodic signals from the master nodefor that data bus. Upon a failure to receive a signal from a master nodewithin an expected time, the slave nodes connected to that data busbegin a wait period (which is preferably a different wait period foreach slave node connected to the data bus). When the wait periodelapses, the slave node determines that a failure in the master node forthe particular data bus has occurred, and takes steps to take over thefunctionality of the master node. Each of the slave nodes is programmedwith a different wait period, so that there is no contention forreplacing the master node when a master node failure has occurred. Inone aspect, backup control of each master node is prioritized, such thatthere is a specific order in which the slave nodes can potentially takeover control of the master node functionality when a failure hasoccurred.

In more detail, again with reference to FIG. 5, one of the nodes 530attached to the main data bus 504 is configured as a master node 503.The other nodes 530 attached to the main data bus 504 (in this examplenumbering four such nodes 530) are configured as first-tier slave nodes523, meaning that they receive but do not transmit master-controlsignals over the main data bus 504. The first-tier slave nodes 523 may,however, from time to time send responsive signals or status signalsover the main data bus 504.

In a preferred embodiment, each of the first-tier slave nodes 523 may beconfigured as a second-tier master node controlling a secondary bus. Onesuch example is shown in FIG. 5, wherein first-tier slave node 523c isconnected to a secondary data bus 513. A plurality of other nodes 530are also attached to the secondary bus data 513, and serve assecond-tier slave nodes 533. There are three such second-tier slavenodes 533 in the example shown in FIG. 5. With respect to the secondarydata bus 513, the first-tier slave/second-tier master node 523ctransmits master-control signals to the second-tier slave nodes 533. Thesecond-tier slave nodes 533 ordinarily operate only in a listen mode,but from time to time may send responsive messages or status messages tothe second-tier master node 523c. The other first-tier slave nodes 523a,523b and 523d may similarly be connected as second-tier master nodes(i.e., cell controllers) each controlling its own secondary bus or cell.

While the control network 501 shown in FIG. 5 has four first-tier slavenodes 523 and three second-tier slave nodes 533, the number offirst-tier slave nodes 523 and second-tier slave nodes 533 is limitedonly by the ability of the master node to communicate with the slavenodes over the particular data bus. There may be more slave nodes orfewer slave nodes on each bus than shown in the control network 501. Ina preferred embodiment, there are no more than eight such cellcontrollers, although more than eight may be used so long as processingcapacity and speed permit.

In addition, further levels of control nesting beyond two data buses mayalso be provided, using a similar approach to the two data bus method.Thus, for example, one or more of the second-tier slave nodes 533 may beconfigured as a third-tier master node controlling its own tertiary orthird-tier data bus. While FIG. 5 only shows two nested control levels,the same control concepts would apply to a control network architecturehaving additional nested control levels.

In a preferred embodiment, communication over the main data bus 504 andthe secondary data bus 513 (or buses, if appropriate) istime-multiplexed such that only one node 530 is transmitting over aparticular data bus at a given time. Usually, each transmitted messagewill be targeted for a specific destination node 530, which may bespecified by address bits in the transmitted message. However, in someembodiments broadcast messages may also be used targeted to multiplenodes 530.

Responsibilities for tasks, or groups of tasks, may be assigned tospecific nodes 530. For example, each of the first-tier slave nodes 223may be assigned a distinct sphere of responsibility. Similarly, each ofthe second-tier slave nodes 533 may be assigned a distinct sphere ofresponsibility. Examples of tasks that may be assigned to differentnodes 530 are described for an exemplary control network later herein,with respect to FIG. 9.

Each of the nodes 530 preferably comprises an uplink transceiver 507, adownlink transceiver 508, and a switch 509. Each of the nodes 530receives signals over its downlink transceiver 508. Over the main databus 504, the first-tier master node 503 transmits master-control signalsto each of the first-tier slave nodes 523. From time to time, accordingto the programmed control protocol, the first-tier slave nodes 523respond to the master-control signals, or otherwise send status messagesto the first-tier master node 503 when events occur specific to thatfirst-tier slave node 523. Otherwise, the first-tier slave nodes 523 donot ordinarily communicate with each other.

In a similar manner, over each secondary data bus (such as secondarydata bus 513), the second-tier master node 523 (for example, first-tierslave/second-tier master node 523c in FIG. 5) transmits master-controlsignals to each of the second-tier slave nodes 533 connected to the samesecondary data bus. From time to time, according to the programmedcontrol protocol, the second-tier slave nodes 533 respond to themaster-control signals, or otherwise send status messages to thesecond-tier master node 523c when events occur specific to thatsecond-tier slave node 533. Otherwise, the second-tier slave nodes 523do not ordinarily communicate with each other.

Communication between nodes is preferably carried out using half-duplextime division multiplexing. In typical operation, the master node pollseach of the slave nodes periodically. Each of the nodes is preferablyprovided with a unique node identification number or address thatdistinguishes it from all other nodes of the control network. The masternode sends a control message to each slave unit in turn, using the nodeidentification number or address to identify the intended destination.Each of the slave nodes receives the control message but only reacts ifit recognizes its own node identification number or address in thecontrol message. The slave node takes the actions requested by thecontrol message received from the master node. Within a designated timeperiod after receiving the control message, the slave node responds tothe master node with an acknowledgment message. Each of the slave nodesare polled in turn so that the master node can keep track of eventshappening throughout the system.

A communication protocol is preferably established so as to avoidcollisions on each of the data buses. A simple and effectivecommunication protocol is one in which the master node for theparticular data bus sends a control message to a particular slave node,which responds with an acknowledgment or status message within apredetermined amount of time before the master node contacts anotherslave node. Slave nodes generally do not initiate communication withoutbeing first polled by the master node. The master node may also send outa broadcast control message that is intended for receipt by more thanone of the slave nodes. The broadcast control message can comprise anode identification number or address that instructs a single particularnode to respond to the broadcast control message. Usually, the singlenode selected for response will be the most critical node requiringreceipt of the broadcast control message.

Failure of the current master node (at any of the control levels)commonly results in the master node either failing to transmit, or elsetransmitting improper control information to the slave nodes over thedata bus. According to a preferred redundant backup control protocol,the slave nodes periodically receive master-control messages from themaster node and, in the event that proper master-control messages failto appear, initiate a failure mode response procedure.

Detection of and response to a failure mode condition may be explainedin greater detail with reference to FIG. 6, which is a block diagram ofa preferred embodiment depicting most of the main components of a node(such as any of nodes 530 shown in FIG. 5). Because failure modedetection and response is carried out by a node 530 operating as a slavenode, the following discussion will assume that the node 603 shown inFIG. 6 is initially configured as a slave node. Further, for simplicityof explanation, it will be assumed that the node 603 shown in FIG. 6 isa first-tier slave/second-tier master node connected to a main bus and asecondary bus (such as first-tier slave/second-tier master node 523cconnected to the main data bus 504 and secondary data bus 513 in FIG.5), although the same node circuit configuration is preferably used foreach of the nodes 530, regardless of control level, for ease ofconstruction and flexibility purposes.

In the node block diagram of FIG. 6, a node 603 is shown connected to afirst bus (e.g., main bus) 604. The node 603 comprises an uplinktransceiver 611, a downlink transceiver 621, a CPU 612 connected to theuplink transceiver 611, and another CPU 622 connected to the downlinktransceiver 621. Both CPUs 612, 622 are preferably connected to adual-port RAM 618, and each CPU 612, 622 is connected to a ROM programstore 614 and 624, respectively. The second CPU 622 is connected throughan appropriate interface to I/O ports 654, which may comprise sensorinputs, control signal outputs, status LEDs, LCD display, keypad, orother types of external connections. It will be understood that the node603 of FIG. 6 can have all the components and functionality of the node301 shown in FIG. 3; however, in FIG. 6 only certain basic componentsneeded for explaining the operation of the invention are depicted.

Each node 603 is preferably capable of both sending and receivingmessages (e.g., control instructions). Typically, the downlinktransceiver 621 operates in a "slave" mode whereby the node 603 receivescontrol instructions using the downlink transceiver 621 and thenresponds thereto, and the uplink transceiver 611 operates in a "master"mode whereby the node 603 issues control instructions (e.g., polls slavenodes) and awaits a response from other nodes after sending such controlinstructions.

The downlink transceiver 621 of the node 603 is connected to a secondarydata bus 652, to which is also connected a plurality of second-tierslave nodes 651 (assuming the node 603 is a first-tier slave/second-tiermaster node). The node 603 thereby functions as a first-tier slave nodewith respect to the main data bus 604, receiving with its uplinktransceiver 611 first-tier master-control signals over the main bus 604from a first-tier master node (such as master node 503 shown in FIG. 5),and also functions as a second-tier master node with respect to thesecondary data bus 652, transmitting second-tier master-control signalswith its downlink transceiver 634 to second-tier slave nodes 651.

The node 603 also comprises a pair of switches 635a, 635b connectedbetween the downlink transceiver 621 and the signal lines 643a, 643b ofthe main data bus 604. In normal operation, the switches 635a, 635bremain open (unless the node 503 is also the first-tier master node,such as master node 503 shown in FIG. 5, in which case the switches635a, 635b would be closed), and the downlink transceiver 621 is therebyisolated from the main data bus 604. However, when a first-tier masternode failure condition is detected, switches 635a, 635b are closed,enabling the downlink transceiver 621 to take over for the first-tiermaster node. The downlink transceiver 621 would therefore functionsimultaneously as master node with respect to both the main data bus 604and the secondary data bus 652.

In a preferred embodiment, detection of a master node failure conditionon the main data bus 604 is accomplished using a timer mechanism, suchas a hardware timer 613 accessible (either directly or indirectly) bythe CPU 612 that is connected to the uplink transceiver 611. Accordingto a preferred control protocol (assuming the node 603 is a first-tierslave/second-tier master node), the uplink transceiver 611 of node 603receives first-tier master-control signals periodically from thefirst-tier master node (such as master node 503 in FIG. 5). Themaster-control signals may, for example, request status information fromthe node 603, or instruct the node 603 to carry out certain control orinput/output functions. The node 603 ordinarily responds by carrying outthe requested functions and/or sending an acknowledgment or statussignal to the first-tier master control node using the uplinktransceiver 611.

Timer 613 times out a wait period between master-control signalsreceived from the first-tier master control node. In a preferredembodiment, each time the uplink transceiver 611 receives amaster-control signal from the first-tier master node that is recognizedas an appropriate master-control signal within the particular programmedcontrol protocol (whether or not the master-control signal is directedto the particular node 603), the CPU 612 connected to the uplinktransceiver 612 resets the timer 613. If the timer 613 ever times out,then CPU 612 responds by asserting a failure mode response procedure.The timing out of timer 613 may result in an interrupt to CPU 612 inorder to inform the CPU 612 of the failure to receive master-controlsignals, or else the CPU 612 may periodically monitor the timer 613 and,when the CPU 612 notices that the timer 613 has timed out, assert afailure mode response procedure.

When a failure mode condition is detected, the CPU 612 sets a failuremode status bit in a predetermined flag location within the dual-portRAM 618. The other CPU 622 periodically monitors the failure mode statusbit in the dual-port RAM 618 and is thereby informed when a failureoccurs. Alternatively, instead of the CPUs 612, 622 communicatingthrough the dual-port RAM 618, timer 613 can directly inform CPU 622when a failure to receive master-control signals has occurred (i.e.,when timer 613 has timed out).

When the CPU 622 has been informed or otherwise determined that afailure mode condition exists, and that the first-tier master node haspresumably failed, the CPU 622 sends a signal over control line 633 toclose switches 635a, 635b, thereby connecting the downlink transceiver621 to the main bus 604. From that point on, the CPU 622 performs as thefirst-tier master node with respect to the main bus 604. The node 603can continue to receive information over the main data bus 604 using theuplink transceiver 611. Alternatively, the node 603 may thereafterperform all transmission and reception over both the main bus 604 andthe secondary bus 652 using the downlink transceiver 621. When thefailure mode is entered, the CPU 622 may be programmed so as to directlycarry out the I/O port functions for which it previously receivedinstructions from the first-tier master node, or the node 603 may sendmaster-control signals to its own uplink transceiver 611 and therebycontinue to carry out the I/O port functions as it had previously beendoing. In other words, the node 603 can give itself control instructionsover the main data bus 604 so that it can continue to perform itspreviously assigned functions. If, after taking over for the first-tiermaster node, the node's downlink transceiver 611 should fail, the node603 can still continue to perform its control functions when the nextslave node takes over control as the new first-tier master node (aslater described herein), because its uplink transceiver 611 continues tofunction in a normal manner.

According to the above described technique, the node 603 therebysubstitutes itself for the first-tier master node upon the detection ofa first-tier master node failure as indicated by the failure to receivethe expected first-tier master-control signals. Should the node 603fail, either before or after taking over control for the first-tiermaster node, the next first-tier slave node would take over and becomethe first-tier master node in a similar manner to that described above.

Referring again to FIG. 5, the order in which the first-tier slave nodes523 take over for the first-tier master node 503 is dictated by the waitperiod timed out by the timer 613 of the particular first-tier slavenode 523. The timer 613 (see FIG. 6) for each first-tier slave node 523is programmed or reset using a different time-out value. A first-tierslave node 523 only asserts a failure mode condition when its internaltimer 613 reaches the particular timeout value programmed for thatparticular node 523.

While the programmed wait periods for the internal timer 613 in eachfirst-tier slave node 523 can vary depending upon the controlapplication, illustrative wait periods are programmed in ten millisecondincrements. Thus, for example, first-tier slave node 523a could beprogrammed with a 10 millisecond wait period; the next first-tier slavenode 523b could be programmed with a 20 millisecond wait period; thenext first-tier slave node 523c could be programmed with a 30millisecond wait period; and the last first-tier slave node 523d couldbe programmed with a 40 millisecond wait period; and so on. First-tierslave node 523a would take over as the first-tier master node if 10milliseconds elapses without it receiving any proper first-tiermaster-control signals; the next first-tier slave node 523b would takeover as the first-tier master node if 20 milliseconds elapses without itreceiving any proper first-tier master-control signals; the nextfirst-tier slave node 523c would take over as the first-tier master nodeif 30 milliseconds elapses without it receiving any proper first-tiermaster-control signals; and so on.

Use of 10 millisecond increments for the wait periods in the aboveexample is considered merely illustrative, and the actual wait periodsshould be selected depending upon the time criticality of the controlmessages, and the number of messages that may be missed before a highenough degree of certainty is established that the master node hasfailed. For example, if a slave node expects to observe acontrol-message signal on the data bus no later than every 5milliseconds, then the slave node may be programmed to assert a failuremode condition after a wait period corresponding to the absence of apredefined number of messages--for example, twenty messages (i.e., 100milliseconds). If critical aspects of the system requiring master nodecontrol need to be serviced in a shorter time period, then the waitperiod would have to be reduced to accommodate the time-sensitivecomponents of the system.

The order in which the slave nodes take over for the master node neednot be dictated by the relative position in the control loop of theslave node with respect to the master node, but rather may be dictatedaccording to the programmed wait period in each slave node. Flexibilityis thereby provided in the order of priority in which the slave nodestake over for the master node in the event of a failure event.

Accordingly, by use of the inventive techniques described herein,redundant backup for the first-tier master node 503 is provided. Suchredundant backup control is provided without requiring additionalphysical nodes to be located within the control system, and withouthaving to provide wiring for such additional physical nodes to the buses504 or 513. The redundant backup for the master node 504 is alsoaccomplished while resolving contention problems that might otherwiseoccur if each of the first-tier slave nodes 523 were programmed with theidentical timeout period.

In a preferred embodiment, redundant backup control is provided in asimilar manner for the secondary data bus 513, and each additional databus that may be provided in the system. Thus, each of the second-tierslave nodes 533 is preferably configured with the circuitry shown fornode 603 in FIG. 6, and each of the second-tier slave nodes 533 cantherefore substitute itself for the first-tier slave/second-tier masternode 523c if the first-tier slave/second-tier master node 523c fails.

If a particular node is operating as a master node for two buses as aresult of a failure of the master node on a higher-tier bus, and thenode operating as such fails, then it is possible that two differentnodes will take over for the failed node, one node taking over on eachbus. For example, supposing that first-tier slave/second-tier masternode 523c has already taken over as the first-tier master node due to afailure of the master node 503, and further suppose that first-tierslave/second-tier master node 523c too fails, then the next first-tierslave node 523d would take over as the first-tier master node withrespect to the main data bus 504, but the first second-tier slave node533a would take over as second-tier master node with respect to thesecondary data bus 513.

In the above manner, despite the failure of one or more nodes,substantial functionality of the control system as a whole can bemaintained. A failed node is essentially discarded or bypassed to theextent possible so as to maintain the highest possible degree ofcontinued operability. Furthermore, because certain parts of the systemwill continue operate despite the failure of the master node,identification of the failed node by engineers or maintenance personnelshould be simplified by being able to identify the inoperative portionof the system that has become isolated due to the failure.

In one aspect, separation of responsibility in each node 603 of masterfunctions and slave functions between two different CPU's each operatingwith a different transceiver allows the node 603 to potentially continueoperating as either a master node or a slave node should one of theCPU's fail, providing that the failure does not disrupt both of thetransceivers at the node 603.

In another aspect of the invention, a simplified single-cable wiringmeans is provided. The wiring means is described herein with particularreference to a two-tier hierarchical distributed control network;however, it will be appreciated by those skilled in the art that theinvention also has applicability to other types of multi-tierhierarchical control networks having multiple buses.

An example of a distributed hierarchical control network 801 inaccordance with one or more aspects of the present invention is depictedin FIG. 8. From a general perspective of information transfer, and asexplained hereinafter more fully with respect to FIGS. 7A, 7B, 8, 9 and10A-10C, the control network 801 comprises two data buses, one data busallowing transfer of information among the first-tier master node andthe first-tier slave nodes, and a second data bus allowing transfer ofinformation among a single second-tier master/first-tier slave node andthe second-tier slave nodes. A particular feature of the control network801 shown in FIG. 8 is that, even though two data buses are defined, thevarious nodes are all interconnected in a loop using only a singlecable.

Preferred cable connectors for implementing the control network 801shown in FIG. 8 are depicted in FIGS. 7A and 7B. The first type of cableconnector 701, designated a "Type A" cable connector, is shown in FIG.7A. The Type A cable connector 701 comprises an insulated cable housinga plurality of wires 704. The Type A cable connector 701 furthercomprises two terminals 703, 705 located at opposite ends of the cablewires 704. Each terminal 703, 705 has a plurality of plugs (e.g., sixplugs) designated as A, B, -, +, A' and B' in FIG. 7A. The wires 704connect the six plugs of terminal 703 in a direct feed-through path tothe six plugs of terminal 705. Internal to the cable connector 701, eachpair of wires 704 may be a shielded, twisted pair; thus, wires 704connecting plugs A and B may comprise a first twisted pair; wires 704connecting plugs - and + (i.e., positive and negative power wires) maycomprise a second twisted pair; and wires 704 connecting plugs A' and B'may comprise a third twisted pair.

The second type of cable connector 751, designated a "Type B" cableconnector, is shown in FIG. 7B. The Type B cable connector 751, similarto the Type A cable connector 701, comprises an insulated cable housinga plurality of wires 754. The Type B cable connector 751 also comprisestwo terminals 753, 755 located at opposite ends of the cable wires 754.Each terminal 753, 755 has a plurality of plugs (e.g., six plugs)designated as A, B, -, +, A' and B' in FIG. 7B. The wires 754 connectthe six plugs of terminal 753 in a crossover path to the six plugs ofterminal 755, with plugs A and B of terminal 753 connected to plugs A'and B' of terminal 755, and plugs A' and B' of terminal 753 connected toplugs A and B of terminal 755. The crossover path may be internal to thecable, or may occur at one of the terminals 753 or 755. Internal to thecable connector 751, each pair of wires 754 may be a shielded, twistedpair; thus, wires 754 connecting plugs A and B of terminal 753 to plugsA' and B' of terminal 755 may comprise a first twisted pair; wires 754connecting plugs - and + may comprise a second twisted pair; and wires754 connecting plugs A' and B' of terminal 753 to plugs A and B ofterminal 755 may comprise a third twisted pair.

As shown in FIG. 8, cable connectors 701 and 751 are used to connectnodes 850 in a loop pattern, with each node 850 connected to two cableconnectors 701 or 751. Each node 850 comprises two terminal interfaces(not shown) each suitable for physically connecting the node to any oneof terminals 703, 705, 753 and 755. Terminals 703, 705, 753 and 755 aretherefore preferably physically constructed in an identical fashion sothat any terminal 703, 705, 753 and 755 can plug into either of theterminal interfaces at any node 850.

The choice of which cable connector 701 or 751 to use in connecting anyone node 850 with the next node 850 depends upon which of the two busesthe latter node 850 is to interact with or, equivalently, which tier ofthe hierarchical control network the latter node 850 is associated with.If two adjacent nodes 850 are part of the same tier (i.e., communicateover the same data bus), then a Type A cable connector 701 (such asshown in FIG. 7A) is used to connect the two nodes 850. If two adjacentnodes 850 are on different tiers (i.e., use different data buses), thena Type B cable connector 751 (such as shown in FIG. 7B) is used toconnect the two nodes 850.

In operation, one pair of wires 704 (or 754) ending at terminal 701 (or751) are connected to the uplink transceiver 611 of a node 850, and theother pair of wires 704 (or 754) ending at terminal 703 (or 753) areconnected to the downlink transceiver 634 of the node. This wiringtechnique is shown in more detail in FIG. 10A, which corresponds to FIG.8 but shows the actual wiring connections in more detail. In FIG. 10A,each node 850 has an uplink transceiver denoted by a "U" and a downlinktransceiver denoted by a "D". Each node 850 is constructed identically,such that the downlink transceiver "D" is connected to one set of plugconnections (e.g., A' and B') and the uplink transceiver "U" isconnected to another set of plug connections (e.g., A and B). The powerwires - and + are not shown for the sake of clarity but are assumed tobe connected as well.

Cable connectors 701 and 751 are then connected between each adjacentpair of nodes 850 to connect the uplink transceivers and downlinktransceivers in such a way that two different data buses areestablished, with the appropriate data bus connected to the appropriatedownlink transceiver "D" or uplink transceiver "U" of a node 850depending upon the node's place in the control network hierarchy. Thus,in the example of FIG. 10A, taking node 803 as the top-level orfirst-tier master node, the downlink transceiver "D" of the first-tiermaster node 803 is connected to the uplink transceiver "U" of the nextadjacent node 810, allowing the first-tier master node 803 tocommunicate in a downlink manner with node 810 over a first bus 861. Acrossover connector, or Type B cable connector 751, is used to connectthe first-tier master node 803 with the next adjacent node 810 to allowthe first bus 861 to be connected in such a manner. If a Type A cableconnector 701 were used instead of a Type B cable connector 751, thenthe downlink transceiver "D" of the first-tier master node 803 would notbe connected to the uplink transceiver "U" of the next adjacent node810, which means that a suitable connection would have to be establishedin some other manner.

Node 810 is then connected to the next adjacent node 811 through a TypeA cable connector 701. This type of connection allows the first bus 861to be connected to the uplink transceiver "U" of the next node 811,thereby permitting downlink communication from the first-tier masternode 803 to node 811. Thus, in the hierarchical network control schemedescribed earlier herein, nodes 810 and 811 may be viewed as first-tierslave nodes of first-tier master node 803.

Node 811 is connected to the next adjacent node 812 through a Type Bcable connector 751. As a result, the first bus 861 is connected to thedownlink transceiver "D" of node 812. In a preferred embodiment, thedownlink transceivers "D" are used only for controlling a lower-leveltier. Consequently, when two downlink transceivers "D" are connectedtogether, no control link is established. In this case, the first-tiermaster node 803 therefore does not directly have a control link withnode 812.

However, node 812 is connected through a Type B cable connector 751 tothe next adjacent node 813, allowing the first bus 861 to be connectedto the uplink transceiver "U" of node 813. The connection of thedownlink transceiver "D" of the first-tier master node 803 with theuplink transceiver "U" of node 813 allows a control link to beestablished between the first-tier master node 803 and node 813.

Thus, in FIG. 10A the first-tier master node 803 establishes a controllink with nodes 810, 811 and 813 over the first date bus 861.

A second bus 862 is used to establish a control link between one of thenodes 850 and the second-tier slave nodes. In the example of FIG. 10A,any of the first-tier slave nodes 810, 811 or 813 may be designated asthe second-tier master node to exercise control using the second databus 862. Selection of the second-tier master node is a matter ofprogramming of the nodes 850.

As an example, node 811 may be designated as the second-tier masternode. The downlink transceiver "D" of node 811 is connected to theuplink transceiver "U" of the next adjacent node 812, therebyestablishing a control link between the second-tier master node 811 andnode 812. A Type B cable connector 751 is used to connect nodes 811 and812 to allow the downlink transceiver "D" of node 811 to be connected tothe uplink transceiver "U" of node 812. At the same time, the Type Bcable connector 751 causes the first data bus 861 to bypass node 812 andreach other nodes 850 downstream.

Node 812 is connected to node 813 through a Type B cable connection 751.As a result, the second data bus 862 bypasses the uplink transceiver "U"of node 813, but the first data bus 861 is connected to the uplinktransceiver "U" of node 813.

FIGS. 10B and 10C show exemplary signal paths for each of the two databuses 861, 862. FIG. 10B shows an exemplary signal path for the firstdata bus 861. The heavy arrows show a signal originating from thedownlink transceiver "D" of the master node 803 and being propagated tothe uplink transceiver "U" of nodes 810, 811 and 813, each of whichreceives information over the first data bus 861. Nodes 810, 811 and 813may also transmit responsive messages over the first data bus 861 usingthe uplink transceiver "U". The heavy arrows also show the signal fromthe master node 803 bypassing node 812, which is a second-tier slavenode.

FIG. 10C shows an exemplary signal path for the second data bus 861. Theheavy arrows in FIG. 10C show a signal originating from second-tiermaster node 811 and being propagated to the uplink transceiver "U" ofsecond-tier slave node 812, and then bypassing first-tier slave node813. The signal continues to propagate in the loop and also bypassesfirst-tier slave node 810. (The first-tier master node 803 may simplyhave its uplink transceiver "U" disconnected, if desired, or mayotherwise be programmed to ignore signals from a second-tier master nodesource).

In one aspect of the invention, the use of Type A and Type B cableconnectors 701 and 751 to connect nodes 850 in a loop pattern serve toestablish multiple separate data buses in a hierarchical controlnetwork. Using a Type A cable connector 701 between two nodes 850results in the two data buses 861, 862 remaining in the same relativepaths. Using a Type B cable connector 751 between two nodes 850 causesthe two data buses 861, 862 to cross over, such that the data busconnected to the downlink transceiver "D" of the previous node will beconnected to the uplink transceiver "U" of the next node, and viceversa. A pattern of Type A and Type B cable connectors 701, 751 may beselected for a given loop so as to effectuate virtually any two-tiercontrol network hierarchy having two data buses.

If more than two data buses are required, as for example where two ormore first-tier slave nodes are to be used as second-tier master nodesfor controlling separate data buses, then an additional pair or pairs ofwires could be provided for each cable connector, and more types ofcable connectors would typically be needed.

FIG. 9 is a conceptual diagram showing the resulting control hierarchyestablished by the choice of cable connectors 701 and 751 shown in FIG.8. Two data buses 911 and 912, each defining a communication path forone tier of the control network, are shown in FIG. 9. The first-tiermaster node 903 (designated by the identifier "MBC" in FIGS. 8 and 9) isshown at the top of the hierarchy, with first-tier slave nodes 904(designated by identifiers "BA", "BB", "CA", "CB", "D", "E" and "FA")shown connected to the first data bus 911. Any of the first-tier slavenodes 904 can be designated as the second-tier master node forcontrolling the second data bus 912. For example, assuming that node 811of FIG. 8 (designated by the identifier "BB" in both FIGS. 8 and 9) isdesignated as the node controlling the second data bus 912, the seconddata bus 912 would be shown as in FIG. 9 as under the control of nodeBB. The second-tier slave nodes 905 are shown also connected to thesecond data bus 912. Whether a node 850 in FIG. 8 or 10A is linked withthe first data bus 911 or second data bus 912 (shown in the conceptualdiagram of FIG. 9) depends, as described previously, on which of thefirst data bus 861 and the second data bus 862 (shown in FIG. 10A) isconnected to the uplink transceiver "U" and which to the downlinktransceiver "D" of the node 850.

The nodes 850 may be physically dispersed within a vehicle or automatedcontrol system so as to carry out input/output or other controlfunctions in an appropriate proximity. The nodes 850, as noted, arepreferably connected in a loop pattern using a single continuous cableconnecting all the nodes 850, with the cable only interrupted by theentry and exit connections at the nodes 850. Use of a single cableminimizes or dispenses with the need for cumbersome junction boxes andor complicated wiring between the nodes. Use of a single cable alsosimplifies assembly and maintenance, and allows rapid isolation offaults, short circuits, and the like.

Cable connectors 701 and 751 may have distinguishing features to enableengineers or maintenance personnel to readily distinguish them. Forexample, they may be outwardly labelled as "Type A" and "Type B," orthey may be of different colors, or else may be distinguished by anyother suitable means.

Connecting the nodes of the control network in a loop pattern using theType A and Type B cable connectors also provides an expedient means forredundant backup control and, more specifically, for slave nodes to takeover for the master node should a failure of the master node occur.Further details of redundant backup control appear in copending U.S.application Ser. No. 08/854,160 entitled "Backup Control Mechanism in aDistributed Control Network," previously incorporated herein byreference.

In a preferred embodiment, the nodes 530 of FIG. 5 are configured withfault isolation and recovery circuitry in the case of a short circuit orsimilar event. Details of such fault isolation and recovery circuitryare described in copending U.S. application Ser. No. 08/853,893 entitled"Fault Isolation and Recovery In A Distributed Control Network,"previously incorporated herein by reference.

While preferred embodiments are disclosed herein, many variations arepossible which remain within the concept and scope of the invention.Such variations would become clear to one of ordinary skill in the artafter inspection of the specification and drawings herein. The inventiontherefore is not to be restricted except within the spirit and scope ofany appended claims.

What is claimed is:
 1. A control network comprising:a plurality ofnodes; and a plurality of cable connectors, said cable connectorsconnecting said nodes in a loop with each node connected to the nextnode in the loop by a single cable connector; said cable connectors eachcarrying at least two signal pairs and being either of a first type or asecond type, the first type of cable connector having a feedthru pathfor both of its two signal pairs, and the second type of cable connectorcrossing its two signal pairs; wherein at least one pair of said nodesis connected by a cable connector of the first type and at least oneother pair of said nodes is connected by a cable connector of the secondtype.
 2. The control network of claim 1 wherein one of said nodesoperates as a master node with respect to one or more of the othernodes.
 3. The control network of claim 1 wherein said signal pairs forall of said cable connectors collectively comprise two data buses. 4.The control network of claim 3 wherein one of said nodes operates as amaster node with respect to a first data bus and a another one of saidnodes operates as a master node with respect to a second data bus. 5.The control network of claim 1 wherein said cable connectors each carrya pair of power wires.
 6. The control network of claim 1 wherein saidfirst type of cable connector and said second type of cable connectoreach have the same physical terminal connection at each end of the cableconnector.
 7. A method for wiring in a distributed, hierarchical controlnetwork having at least a first control tier and a second tier, saidmethod comprising the steps of:connecting a plurality of nodes in aloop, each of said nodes having two data bus input connections and twodata bus output connections, said step of connecting a plurality ofnodes comprising the steps offor each node connection between nodes ofthe same tier level, connecting the data bus connections from one nodeto corresponding data bus connections in the next node; and for eachnode connection between nodes of different tier levels, crossing overthe data bus connections from one node to next node; and communicatingamong said nodes over either a first data bus established by the nodeconnections or a second data bus established by the node connections. 8.The method of claim 7 wherein one of the two data bus input connectionsat each node corresponds to the first data bus and the other correspondsto the second data bus, and wherein one of said two data bus outputconnections at each node corresponds to the first data bus and the othercorresponds to the second data bus.
 9. The method of claim 7 wherein oneof said nodes comprises a first-tier master node, and wherein anotherone of said nodes comprises a second-tier master node.
 10. The method ofclaim 9 wherein said second-tier master node is controlled by saidfirst-tier master node.
 11. A control network comprising:a plurality ofcontrol nodes, each of said control nodes having a node terminal adaptedto receive a cable connector; and a plurality of cable connectors, eachof said cable connectors comprisinga first terminal, a second terminal,and at least two pairs of wires connected between said first terminaland said second terminal, said two pairs of wires being connected in afeedthru configuration if a cable connector is of a first type and beingconnected in a crossover configuration if a cable connector is of asecond type; wherein each node is connected to no more than two othernodes, each node connection using one of said cable connectors such thatat least one cable connector of the first type and at least one cableconnector of the second type is used in connecting said nodes.
 12. Thecontrol network of claim 11 wherein each node is connected to exactlytwo other nodes such that the connections between the nodes form a looppattern.
 13. The control network of claim 11 wherein said nodes andcable connectors collectively comprise a first data bus and a seconddata bus, and wherein said at least two pairs of wires carries signalsover said first data bus and said second data bus.
 14. The controlnetwork of claim 1 wherein one of said nodes is designated a first-tiermaster node and a second one of said slave nodes is designated as asecond-tier master node.
 15. The control network of claim 14 whereinsaid second-tier master node comprises a slave node of said first-tiermaster node.
 16. A control network comprising:a plurality of nodes; anda plurality of cable connectors, said cable connectors connecting saidnodes in a loop with each node connected to the next node in the loop bya single cable connector; said cable connectors each carrying at leasttwo signal pairs and being either of a first type or a second type, thefirst type of cable connector having a feedthru path for both of its twosignal pairs, and the second type of cable connector crossing its twosignal pairs; wherein said signal pairs for all of said cable connectorscollectively comprise two data buses; and wherein one of said nodesoperates as a master node with respect to a first data bus and a anotherone of said nodes operates as a master node with respect to a seconddata bus.
 17. A control network comprising:a plurality of nodes; and aplurality of cable connectors, said cable connectors connecting saidnodes in a loop with each node connected to the next node in the loop bya single cable connector; said cable connectors each carrying at leasttwo signal pairs and being either of a first type or a second type, thefirst type of cable connector having a feedthru path for both of its twosignal pairs, and the second type of cable connector crossing its twosignal pairs; wherein said cable connectors each carry a pair of powerwires.
 18. A control network comprising:a plurality of control nodes,each of said control nodes having a node terminal adapted to receive acable connector; and a plurality of cable connectors, each of said cableconnectors comprisinga first terminal, a second terminal, and at leasttwo pairs of wires connected between said first terminal and said secondterminal, said two pairs of wires being connected in a feedthruconfiguration if a cable connector is of a first type and beingconnected in a crossover configuration if a cable connector is of asecond type; wherein each node is connected to exactly two other nodessuch that the connections between the nodes form a loop pattern, eachnode connection using one of said cable connectors.
 19. A controlnetwork comprising:a plurality of control nodes, each of said controlnodes having a node terminal adapted to receive a cable connector; and aplurality of cable connectors, each of said cable connectors comprisingafirst terminal, a second terminal, and at least two pairs of wiresconnected between said first terminal and said second terminal, said twopairs of wires being connected in a feedthru configuration if a cableconnector is of a first type and being connected in a crossoverconfiguration if a cable connector is of a second type; wherein eachnode is connected to no more than two other nodes, each node connectionusing one of said cable connectors; and wherein one of said nodes isdesignated a first-tier master node and a second one of said slave nodesis designated as a second-tier master node.
 20. A control networkcomprising:a plurality of nodes; and a plurality of cable connectors,said cable connectors connecting said nodes in a loop, with each nodeconnected to the next node in the loop by a cable connector; said cableconnectors each comprising at least two signal paths and being either ofa first type or a second type, the first type of cable connector feedingthru its signal paths, and the second type of cable connector crossingover its signal paths; wherein at least one pair of said nodes isconnected by a cable connector of the first type and at least one otherpair of said nodes is connected by a cable connector of the second type.21. A control network comprising:a plurality of nodes, each node havinga connection to two data buses; a single continuous cable path formed ofa plurality of cable sections, each cable section connecting the databuses between two nodes, wherein the data buses are fed through if thecable section is of a first type or crossed-over if the cable section isof a second type, said single continuous cable path comprising at leastone cable section of the first type and at least one cable section ofthe second type.
 22. The control network of claim 21 wherein each ofsaid nodes comprises two feed-thru signal paths, said two feed-thrusignal paths adapted for connection to a first cable section at a firstend of the two feed-thru signal paths and to a second cable section at asecond end of the two feed-thru signal paths.
 23. The control network ofclaim 21 wherein each of said nodes comprises an uplink transceiverconnected to one of the two data buses and a downlink transceiverconnected to the other of the two data buses.